Hi all

I have a 2012 1.6 Octavia diesel estate, 116,000 miles on the clock. It is serviced as per the schedule every year.

A recent problem has been uneven idling, and this only improves slightly at optimal engine temperature, when cold I have to keep the revs up to stop kangarooing.

I have a VAG scanner and this is showing no problems. Took it to my local garage and their workshop scanner showed the same - only comment was a slight airflow issue. The garage suggested changing the air filter. I found this to be relatively clean as expected, but changed it anyway. Rough idle continues.

I’m no mechanic, but could this be a fuel injector problem ? What could cause this without being picked up on a scan ? All best guesses welcome !

Thanks 

 

Edited 21 February, 20233 yr by Tony12
Correction

I think that can be caused by a dirty throttle body. Easy enough to remove and clean it. Worth cleaning the EGR valve too.

 

Just did both on my VRS. Brake cleaner was OK but carb cleaner seemed stronger and really cleaned them aided by an old toothbrush.

 

Edited 26 February, 20233 yr by FatblokeVRS

https://youtu.be/7BFLJhW8azI

 

@FatblokeVRS

Bear in mind that a diesel engine does not have a throttle body.

Thanks guys. I’m trying Wynns diesel engine system cleaner, poured a bottle in on a quarter tank then filled up to mix it in. I’ll see how that goes over the next couple of weeks, hopefully if it’s mucky jets it’ll clean them out.

3 hours ago, MicMac said:

@FatblokeVRS

Bear in mind that a diesel engine does not have a throttle body.

Most later diesel engines have a motorised butterfly valve that does the job of an anti-shudder valve on switch off and to induce a partial vacuum for EGR, usually referred to as a throttle valve/body.

 

It is the correct term as it does indeed "throttle" the intake air, the common useage of "throttle" for "accelerator" is perhaps the one out of place.

I keep hearing that idea being chucked about also, here is what it is called in VAG parlance and image.

 

 

Could the butterfly valve be responsible for lumpy idling ?

It's unlikely, first see how the fuel cleaner affects things.

 

As you suspect, it's possible the injectors are fouled or just tired.

 

When you add fuel cleaner to tackle running issues rather than just regular cleaning it's a good idea to use it at an increased dosage.

On 27/02/2023 at 18:11, Tony12 said:

Could the butterfly valve be responsible for lumpy idling ?

 

Absolutely! If you also experience shuddering and partial run on sometimes when switching off then its 100% the cause of that and the rough idling.

There’s no shudder or run on, but I’ve had older cars where that’s happened.

Something worrying I’ve noticed is a sort of scorched smell, and today I popped the bonnet and noticed vapor rising from the oil filler cap. The oil level is where it should be, as is the coolant. As stated before, no warning lights on the dash, and my VAG scanner is not throwing up any fault codes. Car is regularly serviced. 
I’ve got the number of a mobile VAG mechanic so I’m thinking of getting him to look at it before something very expensive happens.

Could be a problem with the PCV system not evacuating properly.

Thanks MicMac, I’ll check that out 👍. 

Hi all, just an update on the rough idling problem with my 2012 Octavia diesel. A mobile mechanic brought his scanner and it showed the functioning of each fuel injector as a percentage. One was badly outside its optimum functioning parameter, and a second one close behind. So this imbalance was the cause of the engines rough idling. The quick and least expensive fix is the worn injectors being hydraulically pushed out and replaced. If that fails, and it can, it’s the more expensive option of dismantling part of the engine to do the job. I’m not a mechanic as you might guess, so you’ll know what this involves.

Having spent 1000’s on the suspension already, fixed the clutch, new cam belt and water pump, I think enough is enough for an 11 year old car on 117,000miles. This is not to mention sundry failed electrical switches I’ve replaced myself. This has left me quite disillusioned about the legendary Skoda reliability. My wife’s 2002 Honda served her for 21 years and passed every mot. No major repairs, just annual servicing.

So it’s goodbye Skoda, hello low mileage Toyota hybrid for me !

Adios guys, and thanks for all your help over the past few years ! 👍

 

@Tony12

 

Adios, better luck next time.